This invention relates to a piston-type fluid suspension system and, more particularly, to an assembly for variably adjusting the damping characteristics of the shock absorber during the compression and rebound strokes of the shock absorber piston.
Shock absorbers are used in connection with automobile suspension systems and other vehicle suspension systems to absorb unwanted vibrations which occur during locomotion. To absorb this unwanted vibration, shock absorbers are generally connected between the body and the suspension of the automobile. A piston is located within the shock absorber and is connected to the vehicle body through a piston rod. Because the piston is available to limit the flow of damping fluid within the working chamber of the shock absorber when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which could otherwise be transmitted from the suspension of the automobile to the body.
A conventional double tube shock absorber comprises a pressure tube with a piston therein and a reserve tube surrounding the pressure tube. A piston rod connected to the piston projects from one end of the pressure tube. At the other end of the pressure tube, a valve communicates with the reserve tube. Damping is controlled by orifices in the piston which regulate passage of fluid from one side of the piston to the other. Due to the presence of a piston rod on only one side of the piston, different volumes of hydraulic fluid must be displaced on the compression and rebound strokes. This difference is termed the rod volume. The rod volume of hydraulic fluid is pushed out of the pressure tube during the compression stroke through the valve in the base of the shock absorber. The hydraulic fluid is then stored in the reserve tube which surrounds the pressure tube of the shock absorber. During the rebound stroke, the fluid which was displaced into the reserve tube through the base valve reenters the pressure tube via the same valve. As the piston moves back and forth within the pressure,tube, the rod volume of oil is correspondingly pushed into and out of the reserve tube through the base valve.
In a typical vehicle, the vehicle load primarily depends upon the number of passengers and the amount of cargo. While vehicle suspension systems are typically designed for a nominal load, the actual load at any point in time will vary. Variations in vehicle load cause corresponding variations in the operation of the shock absorbers. When a vehicle is heavily loaded, the typical shock absorber exerts a diminished damping effect on the suspension system because of the increased inertial force of the higher load. Correspondingly, when the vehicle load is less than the nominal load, the shock absorber typically exerts an increased damping effect due to the reduced inertial force effecting the shock absorber. Present shock absorbers do not compensate for varying vehicle loads and, therefore, the suspension system does not react consistently for different vehicle loads. Therefore, it is desirable to provide a shock absorber having a variable damping force which varies in accordance with the load of the vehicle.
Accordingly, it is a primary object of the present invention to provide a shock absorber in which the amount of damping force generated during compression and rebound of the shock absorber varies in accordance with the vehicle load.
Another object of the present invention is to provide a shock absorber whose damping characteristics can be easily and conveniently controlled in accordance with the vehicle load.
Yet another object of the present invention is to provide a pressure responsive valve which modulates fluid flow between the working chamber and the reserve chamber of a shock absorber in order to vary the damping characteristics of the shock absorber during compression and rebound.
A shock absorber according to the present invention has a control valve for variably controlling the damping characteristic of the shock absorber. According to the principles of the present invention, a pressure tube having first and second ends forms a working chamber for storing damping fluid. A reciprocating piston disposed within the working chamber divides the working chamber into an upper and a lower portion working chamber. The piston allows restricted flow of damping fluid between the upper and lower working chambers. A reserve tube surrounds the pressure tube and defines a fluid reservoir for storing damping fluid between the reserve tube and the pressure tube. A fluid reservoir stores the damping fluid, and the pressure tube is disposed therein. An axially extending piston rod having first and second ends is disposed within the pressure tube and connects to the piston at one end. The other end extends through the upper working chamber out one end of the pressure tube. A base valve controls the flow of damping fluid between the lower working chamber and the fluid reservoir. A control valve variably controls the fluid flow between the upper working chamber and the fluid reservoir.
Advantageously, the variable damping valve operates to vary the damping characteristic of the shock absorber in accordance with the vehicle loading. Further, the damping valve varies the ride characteristics of a car depending upon the vehicle load.
Other objects, advantages, and features of the present invention will become apparent to one skilled in the art upon reading the following description and claims, taken in conjunction with the following drawings.